1. Field of the Invention
The present invention related to measurement and design of unique replacement parts for large industrial machine structures.
2. Discussion of Prior Art
It is often necessary to manufacture replacement parts for large, high precision industrial machines such as steam turbines, generators, locomotives, large ships, oil refineries, iron mills, stamping mills, factory tools and other types of large scale machinery which is either impossible or impractical to bring into a shop for in-house measurements. Typically, a large casing structure is to be reused and the internal stationary and rotating parts are to be replaced. In order to manufacture these replacement parts, it is necessary to measure a large number of interior dimensions of the casing.
Several problems exist in making high accuracy measurements on site:
1) the maintenance person do not know which is the proper tool to use; PA1 2) the maintenance person does not know the exact location of dimensions, and/or clearances to measurement; PA1 3) the maintenance person does not know how to properly position the too; PA1 4) the maintenance person inaccurately reads the measurement number; and PA1 5) the maintenance person makes errors in transcribing the measurements during input to a data base or computer system.
The measurement activities often occur during a shut down, or maintenance period, during which the turbine is out of service and disassembled. The owner of the machinery wishes to minimize the length of the shutdown period, since no revenue is produced during the outage. Thus, for a utility, access is allowed for a period of 3-4 days on average. Also, during this access period, personnel measuring the case must share access with many other workers. The restricted `time window` places severe restrictions on the amount of data that can be gathered during the visit.
Much time also goes into preparing a detailed plan of exactly what to measure during the on-site visit. The pre-planning is difficult, since often the interior design of the unit is not known in advance.
Ser. No. 08/888,795 filed Jul. 7, 1997 Allowed, RD-25543 "A Portable Measurement System Using Image and Point Measurement Devices" by Nelson Corby, Christopher Nafis, Boris Yamrom described how to obtain precise measurements of industrial structures, but did not guide the user as to what are the critical clearances to measure, precisely where they were, and how to measure them.
In the course of disassembling, servicing and reassembling large machines, it is necessary to measure and record many dimensions within the machines. An important type of measurement are clearance measurements--i.e. the gaps between rotating and stationary parts. There are hundreds of such clearances to measure and the measurement locations are located all over the machine structure at specific critical places (defined by design engineers). Engineering will also define specific procedures for making these measurements.
In many cases, the parts being replaced represent a new or amended design for the service company. Thus, it is currently necessary for a skilled design engineer to accompany the group to the site and to guide the measurement process. Given the small number of such engineers, it can be difficult to locate and send such a person on short notice.
A further complication is that usually the part designers are not the same people who visited the site and performed the measurements. It would also be desirable to provide the design staff with a method to measure needed dimensions during a later time off-site.
The measurement person is usually not an engineer and will require guidance and help from an onsite supervisor to guide him in locating the measurement locations and in specifying the method of measuring a given clearance. It is often difficult for the supervisor to provide this information from poor quality or confusing paper blueprints.
The usual practice is to employ two man teams--one to make measurements and second to record the data on paper sheets provided by the utility owner or equipment manufacturer. There can be errors in communicating and recording the measurements caused by long working hours, the high noise environment of the power plant and poor penmanship.
Different tools are required to measure different measurements with a high degree of accuracy. Sometimes these tools may be highly accurate for a small measurement, however the accuracy is lost with a larger measurement is made.
Standard measurement tools consist of taper gages, micrometers, calipers, scales, sliding parallel blocks and various plates or sheets of metal. It is often necessary to use auxiliary apparatus such as machinist's squares, gage blocks, ground flat tooling plates etc. to "extend" the range of the measurement tools at hand. This is usually left up to the creativity of the measurement person. Lately, new tools with electronic encoders (to read the measured value) with connection to laptop computers or electronic data logging system have been used to increase the speed and accuracy of reading the tool and storing the measurement.
After all the clearance measurements are made, the supervisor will compare the actual measurements with the expected measurements. These expected values typically come from manufacturers specification sheets or from historical records of the specific machine being serviced. He will compute deviations and enter them on the sheets. The resultant set of papers contains the current set of dimensional data for the machine and the deviations from "ideal" or expected. The supervisor then has to form an opinion as to the "correctness" or state of the machine. If the data indicates correct dimensions, then the final assembly (or dis-assembly) can proceed. It is often difficult for the supervisor to ascertain correct alignments and orientations from the tabular data.
After the service period, the unit is re-assembled and returned to service until the next scheduled shutdown, typically 2-3 years later.
After the on-site visit has concluded, the turbine or generator service company must prepare initial part designs, a price quotation and (if successful in bidding) then prepare detailed manufacturing drawings to guide the manufacture of the replacement parts over the next 12-24 months. At the next opportunity usually 18-24 months later during the next turbine overhaul, the service company returns and installs the new replacement parts. If the parts are incorrect at delivery, then costly on-site machining may be necessary to correct the design. Re-machining on-site may become also very difficult, time consuming and expensive. If re-machining delays the return of the turbine to service, then the service company may incur cost penalties.
Thus, it would be desirable to develop a system that would instruct a user which dimensions to measure through a graphical interface, automate the acquisition and storage of these measurements, and compare these to corresponding engineering specifications and historical data to automate the maintenance process.
Currently, there is the need for a system which accurately instructs a user on what type of tool to use, how to operate the tool, the precise location to apply the tool to make measurements of dimensions and automatically to store the measurements taken.